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Passing parameters to a method called by NSTimer in Swift

Posted by: admin November 30, 2017 Leave a comment

Questions:

I’m trying to pass an argument to a method that is called by NSTimer in my code. It is throwing an exception. This is how I’m doing it. Circle is my custom class.

    var circle = Circle()
    var timer = NSTimer.scheduledTimerWithInterval(1.0, target: self, selector: animate, userInfo: circle, repeats: true)

Below is the method that is being called

    func animate(circle: Circle) -> Void{
      //do stuff with circle
    }

Note: The method is in the same class that it is being called. So I believe i’ve set the target correctly.

Answers:

The selector you use with NSTimer is passed the NSTimer object as it’s one and only parameter. Put the circle object in it as userInfo and you can extract it when the timer fires.

var circle = Circle()
var timer = NSTimer.scheduledTimerWithInterval(1.0, target: self, selector: "animate:", userInfo: circle, repeats: true)

func animate(timer:NSTimer){
  var circle = timer.userInfo as Circle
  //do stuff with circle
}

Questions:
Answers:

Your selector needs to be a string unless that’s supposed to be an ivar. Also, your animate function has the wrong signature. The following changes should get you moving again:

var circle = Circle()
var timer = NSTimer.scheduledTimerWithInterval(1.0, target: self, selector: "animate", userInfo: circle, repeats: true)

func animate(circle: Circle) -> () {
  //do stuff with circle
}

The function really doesn’t need to return the empty tuple; it can be written without the -> ()

I’ve also seen the selector string wrapped in a “Selector()” method: Selector("animate"). It works either way.

I’ve been messing with NSTimer and closures myself and wrote an article on it: Using Swift’s Closures With NSTimer